LTC3101 datasheet(13/34 Pages) LINER

13 / 34 page

LTC3101

3101fb

OPERATION

INTRODUCTION

The LTC3101 provides a complete power management

solution for low power portable devices. It generates a

total of six output voltage rails and provides a seamless,

automatic transition between two input power sources.

The LTC3101 contains three high efﬁciency synchronous

DC/DC converters: a 5-switch buck-boost DC/DC con-

verter and two synchronous 3-switch step-down DC/DC

converters. The buck-boost DC/DC converter is typically

utilized to provide a 3V or 3.3V rail that lies within the

input voltage range. The two step-down converters can

be conﬁgured to provide two lower voltage output rails,

such as a 1.8V rail for SDRAM and a 1.2V rail to supply

the system microprocessor.

The LTC3101 can operate from any power source over the

wide input voltage range of 1.8V to 5.5V. All three switching

DC/DC converters operate from a common 1.27MHz oscil-

lator and a single pin can be used to place all three DC/DC

converters into Burst Mode operation to reduce the total

no-load quiescent current with all six output voltage rails

active to only 38μA (typical). In standby operation, with

only the LDO and MAX outputs active, the input current

is reduced to 15μA (typical).

The 5-switch buck-boost DC/DC converter generates a

user-programmable output voltage rail that can lie within

the voltage range of the input power sources. Utilizing

a proprietary switching algorithm, the buck-boost con-

verter maintains high efﬁciency and low noise operation

with input voltages that are above, below, or even equal

to the required output rail. A protected Hot Swap output

once the buck-boost reaches regulation. This provides a

current-limited output that can be shorted without affecting

the primary buck-boost output. One use of the Hot Swap

output is to power external ﬂash memory cards that need

to be hot-plugged without disrupting the primary buck-

boost output rail.

The synchronous buck converters are typically used to

provide two high efﬁciency lower voltage rails and sup-

port 100% duty cycle operation to extend battery life. The

output voltage of each buck converter is independently

user programmable and can be set as low as 0.6V.

An always-alive LDO provides a ﬁxed 1.8V output at 50mA

which can be utilized to power critical functions such as a

real time clock. Reverse blocking allows the LDO to be used

to charge a supercapacitor for memory retention when both

power sources are removed. The MAX output generates

a secondary always-alive, current-limited output rail that

tracks the higher voltage input power source (battery or

USB) and is convenient for powering additional external

LDOs and circuitry that can function directly from a wide

input voltage range.

A pushbutton interface and internal supply sequencing

complete the LTC3101 as a total power supply solution

while requiring only a minimal number of supporting

external components. Integral to the pushbutton control

is an internal microprocessor reset generator with a reset

duration that can be easily programmed using a single

external capacitor allowing the interface to be customized

to each particular application.

The extensive functionality and ﬂexibility of the LTC3101,

along with its small size and high efﬁciency, make it an

excellent power solution for a wide variety of low power

portable electronic products.

PUSHBUTTON INTERFACE

The LTC3101 includes a pushbutton interface that allows

a single momentary pushbutton to control the sequenced

power-up and power-down of all output rails in coordina-

tion with an external microprocessor. In addition, three

independent enable pins allow an unused DC/DC converter

to be independently disabled and also provide the means

to manually implement an alternate power-up sequence.

The LTC3101 can be enabled by either forcing PWRON

high or by forcing PWRKEY low. In either case, the DC/DC

converters (if enabled by their respective enable pin)

will power up in the internally ﬁxed default sequence:

buck converter 1, buck converter 2, and ﬁnally the buck-

boost converter. In the typical application, the power-on

sequence is initiated when the PWRKEY is driven low by an

external momentary pushbutton. Once the microproces-

sor is powered up it must assert PWRON high before the

pushbutton is released, thereby forcing the LTC3101 to

LTC3101 Datasheet(PDF) 13 Page - Linear Technology

LTC3101 Datasheet(HTML) 13 Page - Linear Technology

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34

Datasheet Download

Link URL